I like to write code listing so that they can be easily copypastad. Please do so at own risk. Some values, links etc. may be out of date. Instead of executing the code listing, you can also follow the instruction from the Arch Wiki Article.

# parameters
date=2018.03.01
iso=archlinux-$date-x86_64.iso
stick=/dev/sdb
point=/mnt/usb0
# download Arch Linux
wget http://mirrors.evowise.com/archlinux/iso/$date/$iso
label=$(isoinfo -i $iso -d | grep "Volume id" | grep -o "\w*$")
# create bootia32.efi
echo "
    insmod part_gpt
    insmod part_msdos
    insmod fat
    insmod efi_gop
    insmod efi_uga
    insmod video_bochs
    insmod video_cirrus
    insmod font

    if loadfont \"${prefix}/fonts/unicode.pf2\" ; then
      insmod gfxterm
      set gfxmode=\"1024x768x32;auto\"
      terminal_input console
      terminal_output gfxterm
    fi

    menuentry \"Arch Linux archiso x86_64\" {
      set gfxpayload=keep
      search --no-floppy --set=root --label $label
      linux /arch/boot/x86_64/vmlinuz archisobasedir=arch archisolabel=$label add_efi_memmap
      initrd /arch/boot/x86_64/archiso.img
    }

    menuentry \"UEFI Shell x86_64 v2\" {
      search --no-floppy --set=root --label $label
      chainloader /EFI/shellx64_v2.efi
    }

    menuentry \"UEFI Shell x86_64 v1\" {
      search --no-floppy --set=root --label $label
      chainloader /EFI/shellx64_v1.efi
    }" > /tmp/grub.cfg
grub-mkstandalone \
    -d /usr/lib/grub/i386-efi/ -O i386-efi\
    --modules="part_gpt part_msdos"\
    --fonts="unicode"\
    --locales="uk"\
    --themes=""\
    -o "/tmp/bootia32.efi"\
    "boot/grub/grub.cfg=/tmp/grub.cfg" -v
# partition and format USB stick
sudo fdisk /dev/sdb << EEOF
g
n



t
1
w
EEOF
sudo partprobe
sudo mkfs.vfat -F 32 -n $label "$stick"1
# copy everything to USB stick
sudo mount "$stick"1 $point
sudo bsdtar xf $iso \
--exclude=isolinux/ \
--exclude=EFI/archiso/ \
--exclude=arch/boot/syslinux/ \
-C $point
sudo cp /tmp/bootia32.efi $point/EFI/boot/bootia32.efi
sync
sudo eject $stick 

During your normal Arch installation you usually come to the point where you install the bootloader. In most cases either GRUB or systemd-boot. We will install GRUB.
For the following commands I assume, you have arch-chroot ed into the installation.
I also assume that /boot will be your EFI System Partition.

pacman -S efibootmgr grub
grub-install \
    --target=i386-efi \
    --efi-directory=/boot \
    --bootloader-id=Archlinux
grub-mkconfig -o /boot/grub/grub.cfg